In the manufacture of glass fiber reinforced thermoplastic resins, glass fibers are generally pretreated with sizing and coupling agents as a means for improving the adhesive strength between the fiber and thermoplastic polymers. Without effective coupling between the glass fiber and the resin, the adhesion between the two will be weak and separation will occur under shear or tensile stresses.
Methods which employ compositions for treating chopped strands for use in short-fiber reinforced thermoplastic resin pellet manufacture are known in the art. For example, U.S. Pat. Nos. 4,369,264, 4,439,558, BE 885,001 describes emulsions of vinyl coupling agents, stable organic peroxides and film forming agents; U.S. Pat. Nos. 4,248,935, 4,358,501, 4,413,085 discloses sizing compositions of aminosilane coupling agents, non-crosslinkable film forming polymers, and anhydride stabilizer agents. When such compositions are employed in treating long glass fibers for use in long fiber reinforced thermoplastic (LFRTP) pellets, the treated glass fibers do not uniformly disperse during the injection molding process due to overly strong adhesion between fiber and resin interface.
Specific methods for treating long glass fibers for use in the preparation of long fiber reinforced thermoplastics have been reported. For example, U.S. Pat. No. 3,862,287 describes a process for the manufacture of long fiber reinforced thermoplastic pellets (Verton.RTM., ICI Corporation), wherein single strands of fibers are passed into a fluidized bed of thermoplastic resin powder. The impregnated fibers are then heated to the melting point of the thermoplastic so that the fiber becomes embedded in the melted thermoplastic matrix. U.S. Pat. No. 4,439,387 describes a method of preparing long fiber reinforced thermoplastic articles (Celstran.RTM., PCI Corporation, U.S.A.) involving co-extrusion of glass fiber and resin through a special die so as to wet the fiber with the molten resin. These methods, however, suffer from a number of deficiencies which include the use of multiple processing steps and expensive specialized equipment. Accordingly, there is a need in the art for a simple, economical method and composition for treating long glass fibers for use in making long fiber-reinforced resin composites and which avoids at least certain of the aforementioned deficiencies.